Reloading a pipeline can hang indefinitely if reloaded configuration has a syntax error.

When running with the ```-r``` flag, and a pipeline is reloaded with a syntax error, the instance of Logstash may never recover.

To reproduce start Logstash with a valid configuration and the ```-r``` option, then break the config by removing a required bracket. The pipeline will attempt to reload and fail (expected). Fix the configuration, the pipeline will not reload the valid configuration (not expected).

Reloading errors of the grammar seems works fine, just syntax error seem to have issues recovering properly.